1. Field of the Invention
The invention relates to a method for processing nonferrous metal hydroxide sludge wastes containing chromium, copper, zinc and nickel as the important nonferrous metals and for simultaneous recovery and separation of the individual nonferrous metals.
2. Description of the Prior Art
The hydroxide sludge wastes which are generally obtained in galvanic processes and in the nonferrous metal processing industry, typically contain the following components (figures refer to percent by weight):
______________________________________ Water 40 to 90, on the average: 70 Iron 0 to 10, on the average: 2 Aluminum 0 to 2, on the average: 0.5 Chromium (III) 0 to 10, on the average: 2 Zinc 0 to 10, on the average: 2 Copper 0 to 5, on the average: 1 Nickel 0 to 5, on the average: 1 Calcium 0 to 20, on the average: 4 Sodium 0 to 2, on the average: 0.5 Silicic Acid 0 to 5, on the average: 1 Cyanide (as a complex) 0 to 0.1, -- Sulfite trace -- Carbonate 0 to 5, Chloride trace, Sulfate trace. ______________________________________
These hydroxide sludge wastes contain a large quantity of water and the content of the valuable metals is too small to allow economical smelting of these wastes. However, the wastes are a burden on the environment and they can only be deposited in special garbage dumps which is very costly. Therefore, a method for cleanly disposing or destroying of these wastes is highly desirable. Even more desirable, on the other hand, would be a method for processing and recovery of the valuable materials and metal values in the waste.
It has been suggested that such wastes be destroyed by admixing them with the raw materials used in the brick production. Furthermore, processing methods from hydrometallurgy and waste water treatment technology are known. However, these methods provide only unsatisfactory recovery of one or two and, hardly ever of more of the materials contained in the waste.
There are also a number of methods for the separation of metals in fixed bed ion exchangers or for their removal from waste water solutions. However, these do not provide for a selective separation of the valuable nonferrous metals and, usually, mixed solutions are obtained which are precipitated collectively and the thus created residue has to be deposited in the form of waste sludge.
A method for recovering copper and zinc from nonferrous scrap metals is known from the the German disclosure Offenlegungsschrift No. 2,340,399 wherein the sludge is leached by means of an ammonium carbonate solution in the presence of oxygen and then the metals are separated from the leaching liquor as copper ammonium carbonate or zinc ammonium carbonate. Such a method cannot be used for the processing of nonferrous metal hydroxide sludge wastes since the content of calcium would disturb the ammonium carbonate equilibrium and, also, chromium hydroxide would remain in the residue.
The liquid-liquid extraction of copper and nickel from ammoniacal solution is known, as is the liquid-liquid extraction of copper at pH values of 1 to 3. These methods are usually performed in combination with electrolysis wherein the final electrolyte is used for stripping off the metal-charged organic phase. Furthermore, there are known methods for extracting zinc from solutions containing sulfuric acid and zinc with the aid of organic liquids and for stripping off the zinc with the aid of an electrolyte in an electrolysis process. All the described extraction methods have a commonality in that the separation can be performed only when the elements iron, calcium, aluminum, and chromium are not present.
Experiments for selectively precipitating the nonferrous compounds from waste sludge have failed because significant amounts of the accompanying elements have been precipitated too.